What is Simple Diffusion?

Diffusion is the net movement of particles of a substance along its concentration gradient - from an area of where the particles are in a high concentration to an area where particles are in a concentration - until equilibrium is established.

Diffusion is a passive process - it does not require the input of energy.

Diffusion occurs in living and non-living systems.

In living systems such as humans, animals and plants, diffusion plays a significant role in the transport of dissolved substances such as gases and digested food products.

Examples of diffusion in living systems are in the table below. Examples of diffusion in non-living systems are found in the demonstrations of diffusion above.

Examples the Diffusion in Living Systems

Example of Diffusion

The removal of carbon dioxide from active respiring tissues

Gaseous Exchange - Oxygen

Gaseous Exchange - Carbon Dioxide

Glucose Transport in the Small Intestine. N.B. some glucose is transported via active transport. If simple diffusion accounted for the only means of transport, a lot of glucose would be lost, given transit time.

From

Tissues. Carbon dioxide is in a high concentration in the tissues as it is produced by aerobic respiration inn cells.

Alveolar Air Space. Inspired air typically has a greater concentration of oxygen than the blood.

Blood in Alveolar Capillaries. Blood flowing to the lungs from the tissues is laden with carbon dioxide and hydrogen carbonate (converted back to carbon dioxide)

Lumen of the Small Intestine. After a meal, chyme entering the lumen of the small intestine has a high concentration of monosaccharides such as glucose.

To

Blood. Carbon dioxide in a low concentration in the blood. as it is constantly removed due the flow of blood away from the tissues and conversion of carbon dioxide into hydrogen carbonate (bicarbonate ions).

Blood in Alveolar Capillaries. The capillaries transport de-oxygenated blood - which has a low oxygen concentration - to the alveoli.

Alveolar Air Space. Inspired air typically has a lower concentration of carbon dioxide than the blood.

Blood in capillary of villus. Any glucose absorned remains in a relatively lower concentration because it is transported y the blood away from the villus.

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